Hazards conditions to human and animal health can occur in swine barns due to sudden bursts of high concentration hydrogen sulfide (H2S) gas released when manure slurry is agitated during removal from deep-pits. Studies show that H2S levels can go from harmless to deadly in a matter of minutes during pit agitation (Patni and Clarke, 2003; Muhlbauer et al., 2008). The goal of this project was to quantify H2S concentrations within various swine housing types and compare these levels to current suggested worker exposure levels. Data collected was also used to investigate the spatial distribution of H2S before, during, and after manure removal events.
A wireless sensor network of hydrogen sulfide sensors coupled with wireless network technology was developed to collect multi-location, near-simultaneous concentration data within swine barns. The network allowed collection of hydrogen sulfide concentration data within a human and/or animal occupied zone. Pem-Tech hydrogen sulfide sensors served as the gas measurement component; this sensor had been validated to perform in swine housing in a previous study to develop a hydrogen sulfide detection system. Sensor data was transmitted on a user-programmed interval using Zigbee wireless network modules. The sensor network was easily transported, installed, and operated by one person. Total component cost for a 12 sensor network was $12,527. The sensor network enabled research on a scale not feasible with the limitations of a mobile lab.
Results confirm the hypothesis that hydrogen sulfide concentrations are highest nearest agitation activity or areas deficient in ventilation. In-barn hydrogen sulfide concentrations increased as agitation activity increased. No agitation resulted in the lowest H2S concentrations during manure pumpouts. Moderate agitation resulted in increased in-barn hydrogen sulfide levels, but the concentrations were much lower than aggressive agitation. If agitation is necessary, minimal, moderate agitation should be used whenever possible to minimize hazardous in-barn H2S conditions.
Hydrogen sulfide levels during current normal operation conditions in the subject deep-pit sow and finish swine barns do not pose as exposure threats to humans or swine. The highest concentration recorded during normal operation of all barns was 2.1 ppm, far below the 10 ppm exposure guideline. This occurred during the winter when barn ventilation was at a minimum. Human and swine exposure did not exceed any exposure guidelines for the monitored normal operation periods inside the barns included in this study. The greatest risk for hydrogen sulfide exposure is when starting agitation. This is when the most gas is contained within the slurry and when mixed this gas is released. Aggressive agitation and agitation which collides with pillars or walls pose the greatest risk for hazardous hydrogen sulfide conditions. No one should ever enter a swine barn during manure agitation, and precautions should be taken to prevent inadvertent entry. Conditions can change rapidly to lethal levels and prevent a worker from escaping. Through careful assessment of environmental conditions and a plan of ventilation and manure agitation management the risks associated with hydrogen sulfide can be reduced.